High-temperature resistor material



Patented Sept. 11, 1923.

UNITED STATES PEENT OFFICE.

NORMAN B. FILLING, OF WILKINSBURG, AND ROBERT E. BEDWORTH, OF PITTSBURGH,

PENNSYLVANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

HIGH-TEMPERATURE RESISTOR MATERIAL.

N0 Drawing.

To all whom. it may concern Be it known that we, NomnN B. Pnmmo, a citizen of the United States, and a resident of \Vilkinsbur in the county of Allegheny and State of ennsylvania, and Romnrr i. Bimivon'rn. a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and usefullmprovemeat in High-Temperature Resistor Material. of which the following is a specification.

This invention relates to resistor material, more particularly to material adapted for use as resistors in furnaces and other heating applications.

Up to the present time, the material in most common use for such applications was an allov of nickle and chromium which has a high inelting point and is well suited for many ordinary heating purposes. However. the alloy, upon exposure, to relat vely high temperaturcs, above 1(i00 C.,espec1a lly in the presence. of air, deteriorates owing to oxidation of the metals of the alloy, and. if the material is in the form of a wire or strip. it is very likely to burn out at the point of high temperature and maximum vaporization.

It. is among the objects of our invention to provide a resistor material having the characteristics desirable for heating and similar applications which may be used at relatively high temperatures in an oxidizing or a neutral atmosphere without deterioration.

It is a further object of this invention to provide a material of the character designated which shall be capable of long oontinucd use at a temperature higher than the ordinary operating temperatures of nicklechromium alloys.

in practising our invention, we provide a non-metallic material, specifically an oxide. having both a low specific resistance and a low negative temperature coeflieient of resistivity. Most oxides are either nonconductors or very poor conductors of electricity at ordinary temperatures and, in order to utilize the same for the passage of electric current, it is necessary to first heat the same to a relatively high temperature by external means and allow current to pass therethrough to maintain the temperature Application filed October 25, 1921. Serial No. 510,316.

of the oxide. Such an application is made of oxides in the well known Nernst lamp.

'0 have found that cadmium oxide has characteristics widely different firom the characteristics of most metal oxides. \Vhereas most oxides havc higih negative tempera ture ooeilicients, cadmium oxide has a very low negative temperature coefficient. The resistivity of cadmium oxide is approximately .1 ohm per cubic centimeter and is practically constant over a large temperature range, which we. have found extends from ordinary room temperatures to 1100 t. and above. The oxide is chemically stable at all temperatures of use. especially at the higher temperatures (500 C. and above) under oxidizing or neutral atmospheric conditions.

The material may be formed into any suitable shapes for various purposes. When used as a resistor in heating furnaces. we preferably grind the cadmium oxide to a fine powder. moisten the same with a small amount of water and compress the material into suitable shapes in molds. The molded articles are then heated to a temperature above 800 (3., causing sintering and cohesion of the particles resulting in a body which is firmly united into a hard. strong and compact mass, capable of withstanding considerable use and rough handling.

.\s an example of the many us s to which our new material is adapted, We have formed the same into tubes which are adapted to replace the ordinary refractory tube or muiile shape having a coil of wire'on the outside thereof for heating purposes. We have also utilized our material in the form of rods and other shapes for heating and for resistors for various purposes.

The material has many advantageous characteristics which make it particularly suitable for resistor elements. It has a very low negative temperature coefiieient, making it. suitable for use at ordinary temperatures as well as at temperatures up to and above 1100 and the resistance thereof is low compared to the resistance of other metal oxides. It has a high melting point, a high dissociation temperature and is stable under oxidizing or neutral atmospheric conditions.

Although we have described our invention in connection with heating furnaces and resistors, it is obvious that the uses of our new material are not limited to those specified but that the range of adaptability thereof includes man other applications. In the above description of our invention, we have described the use of cadmium oxide per se, but it is obvious that modifying elements, such as inert diluting materials, conducting materials or high-resistance materials ma be added thereto to modify the characteristic and fundamental properties thereof for any special purpose. For example, we have modified cadmium oxide with a small amount of inert refractory material, such as zirconium silicate. This is accomplished by grinding the cadmium oxide with about 5% zirconium silicate to a fine powder, moistening the same with water, compressing and then baking the same to produce a hard, tough, coherent mass.

We claim as our invention:

1. Resistor material comprising an oxide having a low negative temperature coefiicient of resistivity.

2. Resistor material comprising an oxide having a low negative temperature coefficient of resistivity over a large temperature range.

3. Resistor material comprising an oxide having a low negative temperature coefficient of resistivity over a temperature range of at least 1000 C.

4. Resistor material comprising an oxide having a low negative temperature coefiicient of resistivity over a temperature range of at least 500 C.

5. Resistor material comprising an oxide having a low negative temperature coefficient of resistivity over a large temperature range and being chemically stable under oxidizing or neutral atmospheric conditions.

6. Resistor material comprising an oxide having a low negative temperature coefficient of resistivity over a large temperature range and being chemically stable under oxidizing or neutral atmospheric conditions to a tem rature of at least 1100 C.

7. esistor material comprising an oxide having a resistivity of approximately .1 ohm r cc.

8. esistor material comprising an oxide having a resistivity of approximately .1 ohm per cc. and havinga low negative temperature coefiicient of resistivity.

9. Resistor material comprising an oxide having a resistivity of approximately .1 ohm per cc. and having a low negative temperature of resistivity over a temperature range of at least 500 C.

10. Resistor material comprising cadmium oxide.

11. Resistor material comprising cadmium oxide and inert refractory material.

12. Resistor material comprising cadmium oxide and a small amount of inert refractory material.

13. Resistor material comprising cadmium oxide and a'small amount of zirconium silicate.

14. Resistor material comprising cadmium oxide and approximately 5% of zirconium silicate.

15. A new article of manufacture comprising a compressed, baked mass of cadmium oxide.

16. A new article of manufacture comprising a compressed, baked mass of cadmium oxide and inert refractory material.

17. A new article of manufacture comprising a compressed, baked mass of cadmium oxide and a small amount of inert refracto material.

18. new article of manufacture comprising a compressed, baked 'mass of cadmium oxide and a small amount of zirconium silicate.

In testimony whereof, we have hereunto subscribed our names this 18th day of October,1921.

NORMAN B. PILLING. ROBERT E. BEDWORTH.

Certificate of Correction.

It is hereby certified that in Letters Patent No. 1,467,810, granted Se tember 11, 1923, upon the application of Norman 13. Filling, of Wilkinsbur an Robert E. Bedworth, of Pittsburgh, Pennsylvania, for an improvement in High-Tempura tune Resistor Materials an error appears in the rinted specification requiring correction as follows: iage 2, line 59, claim 9, be an the word of insert the word coefficient; and that the said Letters Patent should be read with this correction therein that the same mav conform to the record of the case in the Patent Oflioe.

Signed and sealed this 236 day of October, A. 1)., 1923.

[emu] WM. A. KINNAN,

Acting Commissioner of Patents. 

